diff --git a/inventory.lua b/inventory.lua
index 6fae10b..1fc6aae 100644
--- a/inventory.lua
+++ b/inventory.lua
@@ -9,6 +9,25 @@ yl_speak_up.get_inventory_save_path = function(n_id)
 end
 
 
+-- check if stack contains any metadata; return true if it does
+-- (trade_simple does not allow used items or those with metadata)
+yl_speak_up.check_stack_has_meta = function(player, stack)
+	local meta = stack:get_meta()
+	for k, v in pairs(meta:to_table()) do
+		-- the name "fields" is allowed - as long as it is empty
+		if(k ~= "fields") then
+			return true
+		end
+		for k2, v2 in pairs(v) do
+			if(k2) then
+				return true
+			end
+		end
+	end
+	return false
+end
+
+
 -- access the inventory of the NPC (only possible for players with the right priv)
 yl_speak_up.get_fs_inventory = function(player)
 	if(not(player)) then
@@ -95,23 +114,11 @@ yl_speak_up.load_npc_inventory = function(n_id)
 				return 0
 			end
 			-- items with metadata cannot be traded
-			local meta = stack:get_meta()
-			for k, v in pairs(meta:to_table()) do
-				if(k ~= "fields") then
-					minetest.chat_send_player(player:get_player_name(),
-								"Your NPC cannot sell items that contain "..
-								"additional (meta-) data.")
-					return 0
-				else
-					for k2, v2 in pairs(v) do
-						if(k2) then
-							minetest.chat_send_player(player:get_player_name(),
-								"Your NPC cannot sell items that contain "..
-								"additional (meta-) data.")
-							return 0
-						end
-					end
-				end
+			if(yl_speak_up.check_stack_has_meta(player, stack)) then
+				minetest.chat_send_player(player:get_player_name(),
+					"Your NPC cannot sell items that contain "..
+					"additional (meta-) data.")
+				return 0
 			end
 			return stack:get_count()
 		end,